1. Field of the Invention
The present invention relates to a method of manufacturing an organic electroluminescence (EL) display device.
2. Description of the Related Art
A generally known display device having organic EL elements mounted thereon is a device in which pixels each having a single or a plurality of organic EL elements are arranged in a predetermined pattern. By those pixels, a display region of the display device is two-dimensionally divided with high definition. The organic EL elements in the pixels are electronic elements which output, for example, any one of red light, green light, and blue light. A display device having organic EL elements mounted thereon obtains a full-color image by driving the organic EL elements for outputting desired colors at desired emission intensities.
Under such circumstances, a method of producing a display device having a fine organic EL element with high definition by a photolithography process is proposed. Japanese Patent No. 3839276 proposes a method involving forming a photoresist into a film directly on an emission layer. When the method is adopted, the photoresist to be used generally contains large amounts of a photoinitiator, a crosslinking agent, and the like. Here, the photoinitiator, the crosslinking agent, and the like are each a material for changing insolubility at least in a developer. Japanese Patent No. 4507759 proposes a method involving providing an intermediate layer formed of a water-soluble material on an organic compound layer, and patterning the organic compound layer by performing photolithography on the intermediate layer. Here, a water-soluble polymer for constituting the intermediate layer to be formed on an emission layer is generally insulative. In addition, Japanese Patent No. 4544811 proposes such a technology that a water-soluble polymer is used as a peeling layer and a photoresist is stripped together with the peeling layer. In addition, Japanese Patent No. 4736923 proposes a method involving dropping, to a surface of an EL layer (organic compound layer), a solvent (such as chlorobenzene or ethyl acetate) capable of dissolving a photoresist residue remaining on the organic compound layer and rotating the resultant with a spin coater to wash a surface layer portion of the EL layer.
A resist, intermediate layer, peeling layer, or the like to be used in the related art is generally insulative. Accordingly, when part of such layer remains as a residue on the surface of, for example, an emission layer constituting an organic EL element, the residue serves as a resistance to remarkably degrade the element characteristics of the organic EL element in an organic EL display device. Accordingly, upon performance of the patterning of an organic compound layer involving employing a photolithography method, the residue of the resist, intermediate layer, peeling layer, or the like needs to be removed so as not to remain on the surface of the emission layer or the like. However, when a polymer material is used as a constituent material for the resist, intermediate layer, peeling layer, or the like, it is generally difficult to sufficiently remove the material and the residue of the polymer material that cannot be completely removed remains in the device to some extent. This results from the adsorption of the polymer material to a film surface caused as described below. The polymer material is formed as a result of the bonding of an extremely large number of monomers, and hence once the material adheres to the film surface, the film surface and a polymer chain undergo an intermolecular interaction to cause the adsorption. Even when part of the polymer chain separates from the film surface, the probability that the polymer chain adheres to the film surface again is high owing to the adsorption as long as the entirety of the polymer chain does not separate from the film surface, and probably because of the foregoing, the residue of the polymer material cannot be easily removed. Therefore, the following problem has existed heretofore. The element characteristics of organic EL elements in an organic EL display device produced by patterning involving utilizing a photolithography process are inferior to the element characteristics of organic EL elements formed into a pattern with a metal mask or the like in a vacuum in-situ fashion.